<?php
header("Content-Type: text/html;charset=utf-8");
echo '<select  id="marca">';
$bd_host = "localhost"; 
$bd_usuario = "root"; 
$bd_password = ""; 
$bd_base = "centroservicios"; 
$con = mysql_connect($bd_host, $bd_usuario, $bd_password); 
mysql_select_db($bd_base, $con); 
mysql_query("SET NAMES 'utf8'");
$consulta = mysql_query("SELECT * FROM marcas",$con);
if($_GET['c']=="Cargo")
{
	while($fila = mysql_fetch_array($consulta)){	
		
			echo "<option value='".$fila['idMarcas']."'>".$fila['marca']."</option>";
		
	}
}else{
	$convenio="Si";
while($fila = mysql_fetch_array($consulta)){	
		if($fila['convenio'] == $convenio){
			echo "<option value='".$fila['idMarcas']."'>".$fila['marca']."</option>";;
		}
	}
}

mysql_close($con);
echo '</select>';
?>